Surface Chemistry Matters. How Ligands Influence Excited State Interactions between CsPbBr₃ and Methyl Viologen

The photocatalytic properties of cesium lead bromide (CsPbBr 3 ) perovskite nanocrystals make them attractive for designing light harvesting assemblies. Often ignored, the surface chemistry can dictate the excited state interactions of these semiconductor nanocrystals with charge-shuttling redox molecules. We have now explored the impact of CsPbBr 3 nanocrystal surface modification on the excited state interactions with methyl viologen (MV 2+ ) for three different ligand environments: prototypical oleic acid/oleylamine (OA/OAm) ligands, PbSO 4 -oleate capping, and didodecyldimethylammonium bromide (DDAB) ligands. Native OA/OAm ligands and PbSO 4 -oleate capping exhibit the strongest complexation with MV 2+, whereas the bulky DDAB ligand environment shows an order of magnitude weaker complexation. The electron transfer rate constants as measured from transient absorption spectroscopy vary in the range of 1.2–3.6 × 10 11 s –1 for different ligand environments. For DDAB-CsPbBr 3 NCs, the efficiency of electron transfer (Φ et ) is 73%. Despite a protective capping layer, PbSO 4 -oleate capped CsPbBr 3 maintains a redox-active surface which is viable for photocatalytic applications. These results highlight the impact of surface chemistry on excited state interactions of CsPbBr 3 NCs and photocatalytic applications.